1. Field of the Invention
The invention relates to a polygon headed wrench for use in tightening and releasing socket head bolts.
2. Description of the Prior Art
This kind of polygon headed wrench used hitherto is exemplified in FIG. 9. The polygon headed wrench comprises a shank 101, a neck 102 and a head 103 Formed integrally and coaxially with each other along the central axis 100. The head 103 has curved surfaces 104 in the same number as the corresponding surfaces of the shank 101, the center of curvature of the curved surfaces 104 being set on the central axis 100 and the surface of the neck 102 being curved inwardly.
The conventional polygon headed wrench may be used in a first manner of filling the head 103 into the hexagon socket head bolt 105 with the central axis of the wrench being aligned with the central axis 106 of the bolt 105, and in a second manner, as shown FIG. 10, with the central axis 100 being slanted in the extent of inclination .alpha.1 from the bolt central axis 106.
In either manner of use, the conventional wrench has merely smaller contact areas between the curved surfaces 104 of the head 103 and the inner surface the bolt 105. The curved surfaces 104 to contact with the bolt inner surface 107 are relatively easily worn due to repeated use of the wrench, so that the wrench will have relative slip between Lie curved surfaces 104 and the inner surface 107 and not produce Lightening torque and releasing torque. When the curved surfaces 104 are further worn, the wrench runs idle to be unusable. That is, the conventional polygon headed wrench has the problem of a brief span of life.
Another polygon headed wrench which has been proposed in Japanese Utility Model Publication No. Sho 60-19895 is exemplified in FIG. 11. The polygon headed wrench comprises a shank 201, a neck 202 and a head 203 formed integrally and coaxially with each other along the central axis 200. The head 203 has curved surfaces 204 in the same number as the corresponding surfaces of the shank 201, flat surfaces 205 extending in parallel to the central axis 200 and another fiat surfaces 206 extending slantwise with respect to the central axis 200. The center of curvature of the curved surfaces 204 are set at a point displaced from the central axis 200. The slanted flat surfaces 206 slant nearer the central axis 200 as extending to the neck 202, and the surfaces of the neck 202 slant further away from the central axis 200 as extending to the shank 201.
This polygon headed wrench does, similarly with the foregoing wrench shown in FIGS. 9 and 10, have merely smaller contact areas between the slanted flat surfaces 206 of the head 203 and the .inner surface of the hexagon socket head bolt 105. This is because even when such wrench is designed of the head 203 to allow the wrench to be usable with the central axis 200 being slanted at relatively large inclination (30.degree.) with respect to the central axis 106 of the bolt 105, the wrench has only the slanted flat surfaces 206 between the flat surfaces 205 and the neck 202. When the head 203 is otherwise designed to allow the wrench to be usable with the central axis 200 being slanted at inclination .alpha..sup.2 (15.degree.) with respect to the bolt central axis 106 as shown in FIG. 12, the curved surfaces 204 and the slanted flat surfaces 206 become largely different from each other in their contact areas with the inner surface 107 of the hexagon socket head bolt 105. Such unbalance of the contact areas leads to larger wear of the curved surfaces 204 having smaller contact areas, resulting in a short life of the polygon headed wrench. That is, the polygon headed wrench proposed in the Japanese reference has the same problem of a brief span of life as of the foregoing conventional wrench shown FIGS. 9 and 10.